Cathode ray tube heterodyne detector



Jan. 22, 1935.

c. w. HANsELL CATHODE TUBE HETERODYNE DETECTOR 2 sheets-sheet 1 Filed Jan. 16 1930 nhl Lilli lvglli-mlllllmll@mm-w- Lugllrldlllfwlqllnulwlllllllxyllulw -4llllllllh- INVENTOR CLARENCE W. HANSELL MMM ATTORNEY Jan. 22, 1935. W HANSELL 1,988,621

CATHODE RAY TUBE HETERODYNE DETECTOR Filed Jan. 1e, 195o z'sneets-sheet'z Lm i INVENTOR CLARENCE NA HANSELL BY gfwvbt/ ATTORN EY Patented Jan. 22, 1935 CATHODE RAY TUBE HETEODYNE VDETECTOR l Clarence W. Hansell, Port Jefferson, N. Y.,'as

signor to Radio Corporation of America, a corporation o! Delaware Application January 16,r

1930, Serial No. 421,120

1e claims. (c1. 25o-zo) My present invention relates to detectors, and more particularly to heterodyne detector circuits embodying space discharge devices of the cathode ray tube type, the detector circuits being such that the output is much less affected by undesired emission variations, than the circuits now in common use.

In my United States Patent No. 1,850,104, grant-` ed March 22, 1932, there has been disclosed a cathode ray tube for eliminating tube noises in the nal output of high frequency energy amplifiers, which noises arise because of cathodeemission variations, the tube permitting greater radio frequency amplification to be used so that smaller values of radio frequency energy can be amplified successfully. Briefly, this patent discloses an amplifier circuit which comprises a cathode ray tube including a cathode, a plurality of anodes electrostatically shielded from the cathode, the anodes being connected in such a manner that variations in emission from the cathode result in equal and opposite variations in the anode output circuit whereby the disturbing anode currents balance outand much less noise is present in the output of the amplifier.

In another United States Patent No. 1,938,331, granted December 5, 1933, I have disclosed acircuit, including a cathode ray tube, for detecting amplitude modulated carrier waves, the circuit being relatively free from tube noises, and consequently increasing the range of useful signal detection and reception. i

I have found that the cathode ray tube referred to above may be employed in a detector circuit employing the heterodyne principle. Such a heterodyne detector circuit is particularly adapted for use in receiving continuous wave signals, and, also, for reception of modulated carrier waves such as are utilized in radio broadcasting.

Accordingly, one of the main objects of the present invention is to provide a heterodyne detector. circuit employing a cathode ray tube in which the radio frequency energy is applied to the control electrodes, While the local heterodyne energy is also applied to the control electrodes in such a manner that as the two frequencies beat together the average pull exerted on the stream of electrons emitted from the cathode alternates at a frequency equal to the beat frequency between the signal and local frequencies, the anode circuit of the tube being arranged to reduce tube noises due to emission variation. y

Another important object of the invention is to provide a method of operating a cathode ray tube heterodyne detector circuit which consists in applying incoming signal energy to the control electrodes of the tube in push-pull fashion, impressing local energy of a different frequency upon the said electrodes in push-push arrangement, or in reversed order when desired, and connecting the anodes of the tube in push-pull arrangement whereby tube noises are eliminated from the anode circuit and the average current to the anodes varies differentially to produce a useful output at the beat frequency of the signal and local 10 frequencies.

Other objects of the invention are to improve generally the sensitivity and eiiiciency of heterodyne detector circuits by embodying cathode ray tubes, and to, further, provide a heterodyne detec- 15 tor applicable to reception of continuouswaves and modulated carrier waves which is not only less subject to noise, distortion and feed-back troubles but reduces the possibilities of undesired beat frequencies yfrom interference. 20

The novel features which I believe to be characteristic ofmy invention are set forth with particularity in the appended claims, the invention, itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken'in connection with the drawings in which I have indicated diagrammatically several circuit organizations whereby my invention may be'carried into effect.

In the drawings,

Fig. 1 shows a preferred form of heterodyne detector circuit, Figs. 2, 3 and 4 show modified forms of the circuit arrangement of Fig. 1.

Referring to the accompanying drawings in which like characters of reference indicate the same elements in the different figures, there are shown two circuits which permit the balancing' out of tube noise in the output of a heterodyne detector, particularly the noises due to variations in filament emission and initial electron emission velocity. Inasmuch as I have described the cathode ray tube employed in these circuits in greater detail in both the aforementioned copendng applications, I will, at this time, describe only the essential elements of this type of tube.

In Fig. 1, which is the preferred form of -heterodyne detector circuit, there is shown a receiver stage, the input of which stage is coupled to a source of incoming signal energy generally designated as incoming radio signal. The input circuit of the cathode ray tube includes an inductance 1 which is coupled, as at M, to the source of incoming energy, and a pair of variable capacities, 2 and 3, connected in series across the inductance 1. Normally these capacities will be of equal value and will be controlled by a single shaft or other control element.

A source of local energy 4 is connected to the input circuit of the tube in push-push or parallel connection. In some instances it may be expedi ent to apply the incoming radio signal in pushpush relation to the control elements of the tube and the local oscillator energy in push-pull relation. In practice, either arrangement may be used depending on the design of associated equipment. In this case it will be noted. that the incoming radio frequency energy to be detected is applied in push-pull or series connection to the control electrodes, the input circuit of the cathode ray tube being tuned to resonance by the variable capacities 2 and 3. i

The cathode-ray tube as in my aforementioned patents consists of a pair of control electrodes 13, 13', a cathode 8, a pair of anodes'9, 9' connected in push-pull arrangement to a source of'anode current B, and a screen grid, or electrostatic shielding, member l0 connected to a metallic envelope, the latter having aillxed to its exterior a metallic shielding and supporting disk 14 which is connected to the positive terminal of a battery D for biasing the screen grid member 10.

The control electrodes 13, 13.are connected by a lead 15 to the negative terminal of a source of current E, and a metallic envelope 20 is negatively biased from the negative terminal of the source C through a lead 2l. The cathode 8 is energized from a source of current A, the midpoint of which is connected through a lead 22 to a connection between the positive terminal ofN source E and the negative terminal of, source D' and grounded.

A pair of capacities 24, 24', connected in series, are connected across the cathode legs, the connection between the capacities being connected to ground for short circuiting radio frequency currents, and to one of the leads from the local oscillator output. 'Ihe other lead of 4the local oscillator output is connected between the capacities 2 and 3. The inductance 30 in the output circuit of the tube has connected across it a pair of capacities 31, 31' for short circuiting currents of radio frequency, which are connected in series, the connection` between the capacities being grounded. The indutance 30 is the primary of an audio transformer A', which has its secondary connected to any subsequent circuit for utilizing the beat frequency, such a utilizing circuit being one or more stages of beatfrequency amplication, or even head phones.

For heterodyne detection a circuit arrangement as shown in Fig. l should be most satisfactory. In this arrangement the incoming radio frequency energy to be detected is applied in push-pull or series connection to the control electrodes, while the local frequency is applied in push-push or parallel connection. If the two radio frequencies beatv together, first one and then the other control electrode has the sum of two radio frequency energies on it. Then, due to the asymmetrical characteristic of the tube the average pull exerted on the stream of electrons 32 (shown in dotted lines) by the control electrodes alternates from one electrode to the other at a rate corresponding to the beat frequency between the two radio frequency energies. Therefore, the average current to the anodes varies differentially to produce a useful output at the beat frequency. It will be understood, as explained in the aforementioned patents, that the anode circuit is arranged in push-pull manner, whereby equal variations in the anode currents due to the usual source of tube noise will balance out, and no noises due to'energy variation will be heard in the beat frequency output circuit.

Of course, the source of signals to be detected and the oscillating frequency source can be interchanged in so far as their relation to the detector circuit is concerned. It is also possible to combine the signal to be received, and the energy from the local beating oscillator in the input circuit of a detector arrangement adapted to receive amplitude modulated carrier Waves, such a circuit embodying a cathode ray tube having been disclosed and claimed in one of my aforementioned patents. However, the circuit shown in Fig. 1 is preferred for heterodyne reception because it reduces the possibilities of undesired beat frequencies from interference. It also reduces v even harmonic distortion of the output from the tube, and is less subject to noise, 'distortion and feed-back troubles.

In Fig. 2, I have shown a modified form of heterodyne detector circuit arrangement which can be used for receiving continuous wave signals z or modulated carrier wavesl by the heterodyne principle. As in the case of Fig. 1, the signal enyergy and local energy are impressed upon the input circuit of the cathode ray tube. In this modification, however, the output from the local oscillator 4 is inductively coupled as at M to the inductance 1 in the input circuit of the tube.

As in the case of Fig. 1, the signal energy is impressed upon the inductance l by inductive coupling as at M. The input circuit of this modi fication, further, includes a pair of condensers 2 and 3', both variable, and connected in series across the inductance 1. Of course, a single condenser may be used as well. The low potential side of the inductance l is connected to ground through a capacity 2. The control electrode 13 is connected to the negative terminal of the source E, while the control electrode 13 is connected through the coil l to the same or some other point on the source E by the lead 15. Ordinarily, the potentials of electrodes 13 and 13 and the strength of the energy from the local oscillator will be adjusted to give maximum sensitivity and minimum tube noise.

Instead of employing an independent source for I' local energy, the cathode ray tube may be arranged for oscillation to obtain autodyne detecl tion by tuning the anode circuit as well as the control circuit and employing a variable coupling from the output circuit to the input circuit in a manner similar to the autodyne detector employing the usual form of vacuum tube.

More specifically, the arrangement of Figure 2 may be adapted to autodyne reception by merely disconnecting the source 4 and inductively relating the windings 1 and 30 to the extent necessary to produce sustained oscillations.

In 'Figure 3 has been shown a preferred form of an autodyne demodulation circuit which includes the electrodes ofA a cathode ray tube. As will be obvious by mere inspection of this circuit, the arrangement is, in many respects, similar to the arrangement shown heretofore. In this arrangement, however, an inductance L or inductances L and L is or are connected in series with the anodes 9 of the cathode ray tube, as shown, and variably inductively related to the inductance l connected with the electrodes 13 and 13.

In some cases one of the inductances L or L is suflcient to produce the result desired. The oscillations generated, due to this coupling effect, beat with the incoming radio signal to accomplish demodulation of the same in a well known manner. Substantially the same result may be obtained by capacitively coupling the anode circuit to the cathode circuit by a variable capacity C as indicated in Figure 4. .f A

While I have shown several circuits by means of which autodyne detection of signals may be accomplished with a cathode ray tube, it will be understood that I do not intend to limit -myself thereby since,l obviously, many other detailed regenerative combination circuits may be used, in addition to the ones shown, without departing from the spirit of the present invention. On the other hand, it will be understood that I intend to cover broadly the use of any form of regenerative feedback oscillation for autodyne reception by means of a cathode ray tube.

Again, the circuit shown in Fig. 1 can be readily adapted to respond to phase differences between two equal frequencies, and can then be employed as an actuating device in an automatic tuning scheme, as a detector of signal sent by phase modulation, as a means for maintaining synchronism, or it can be used with suitable instruments as a phase indicator equivalent to the common synchroscope. The employment of a cathode ray tube in circuits as shown vherein greatly improves the superheterodyne type of broadcast receiver by increasingits sensitivity and by reducing the background of noise.

While I have indicated and described several systems for carrying my invention intoeifect, it

will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of my invention as set forth in the appended claims. In particular, I wish to point out that the detail proportions and construction of the cathode ray tube and associated circuits shown willundoubtedly be modifled by careful considerations ofy detailed design and to permit of constructing -the tube with less practical diiliculties.

What I Aclaim is:

1. An autodyne detector circuit comprising a cathode ray typeV of vacuum tube having an input circuit and an output circuit, said input circuit being tunable to incoming signals of radio frequency currents, and variable radio frequency feed-back from the output to Ithe input circuit by which the tube can be made to oscillate and produce beats between the incoming radio frequency signal currents and the oscillation currents in a manner to cause an output from the tube at the beat or difference frequency.

2. A method of radio frequency reception which comprises emitting a stream of electrons towards a pair of anodes connected in a symmetrical output circuit, confining said stream between a pair of control electrodes at a predetermined mean position, impressing radio frequency currents upon said control electrodes, applying local oscillations to said control electrodes whereby said stream is deected from said position by an alternating force having a frequency equal to the beat'frequency between the local and radio oscillations, and electrostatically shielding said anodes from said control electrodes.

3. A method of heterodyne reception which comprises applying incoming signal energy to a pair of normally differentially direct current biased control electrodes in a tube, emitting a stream of electrons from a cathode towards a pair of anodes electrically balanced for variations in electron emission, conning said stream at a mean, position between the control electrodes, impressing local energy of a different frequency upon the control electrodes whereby said stream is periodically deflected and the average current in the anode circuit varies differentially to produce a current at the beat frequency of the signal and local frequencies.

4. Means for demodulating electrical oscillations including, a cathode ray tube having a plurality of anodes, a symmetrical output circuit connected between said anodes, a plurality of control electrodes, a cathode, a compound input circuit connected between said control electrodes and said cathode, means for tuning a portion of said input circuit to signal frequency, and means for impressing oscillations at a frequency other than said signal frequency on another portion of said input circuit.

5. Means for heterodyning electrical oscillations including, a cathode ray electron discharge device having a cathode, a plurality of anodes equidistant from said cathode, and a plurality of Acontrbl electrodes includingfa symmetrical circuit connecting said anodes to each other and to lsaid cathode, a source of potential in a common portion of said circuit, a compound input circuit connected between at least one of said control electrodes and said cathode, means for tuning a vportion of said compound circuit to signal frequency, means for maintaining each of said control electrodes at a negative direct current potential with respect to said cathode, and means for impressing oscillations at a frequency other than signal frequency on said input circuit.

6. Means for producing a signal modulated beat frequency current including, a cathode ray elctron discharge device having a plurality of anodes, a plurality of control electrodes, an emission element substantially equidistant .from each of said anodes, and a screening electrodev interposed between said anodes and said cathodes including, a symmetrical circuit connecting said anodes to said cathodes, means for applying direct current potential to said anodes, means for applying a different potential to said screening electrode, an input circuit connecting at least one of said control electrodes tol said cathode,and means for applying signal oscillations and .oscillations at a frequency other than the signal frequency to said input circuit.

7. A heterodyne detector comprising an envelope including a plurality of anodes, a plurality of control electrodes, an emission element spaced equidistant from each anode, means for applying direct current potential to each anode, a compound input circuit including a tuned inductance connected between at least one `of said control electrodes and said emission element, means for applying a different direct current potential between each control electrode and said emission 'element, and means for impressing signal oscillations and oscillations from a local oscillator on said input circuit.

8. Means foiheterodyning signal modulated high frequency current including a thermionic tube comprising a plurality pf anodes, a plurality of control electrodes symmetrically arranged with respect to said anodes, a cathode equidistant from each anode, a screening grid located between said control electrodes and said anodes, a symmetrical circuit including means for applying substantially the .same direct current potential to each of said anodes, means for applying a direct current portential between said screening electrode and said anodes, and means for applying a direct current potential between each of said control electrodes and said cathode.

9. A thermionic demodulator of the heterodyne 'type including, a discharge device having a plurality of anodes, a plurality of control electrodes, a cathode, means for applying the same direct current potential between each anode and said cathode, a repeater circuit symmetrically connected between said anodes, a compound input circuit associated with said control electrodes and said cathode, means for setting up signal oscillations in said compound circuit, means for impressing local oscillations on said compound 'circuit, and means for applying a dfferent direct current potential to each of said control electrodes.

10. A heterodyne demodulation device including, an emission element, a plurality of anodes equally spaced from said emission elementa control electrode, a screen grid electrode interposed between said anodes and said cathode, an output 'circuit connected between said anodes, a compound input circuit connected between said cathode and said control electrode, means for tuning a portion of said input circuit to signal frequency, and means for applying biasing potentials to each of said electrodes.

11. A method of demodulating signals by a heterodyne system including, a cathode ray tube having a cathode, a pair of spaced grid electrodes, and a pair of anodes, which comprises energizing in opposition the control grids of said tube at the frequency of the incoming signals, energizing the control grids of said tube by energy of a frequency different than the frequency of the incoming signals, and feeding the resultant energy from the anodes of said tubes in opposi- V tion.

12. In combination a cathode ray tube having a pair of anodes and a pair of control grids, a tun- -able input circuit responsive to radio frequency put circuit responsive to the difference frequency of the signal and local oscillators, said output circuit being connected to said anodes, and means for differentially biasing said control grids whereby the beating together o1' the two radio frequencies produces a component of output current at the difference frequency.

13. In a. system employing a cathode ray tube having a cathode, a pair of symmetrically spaced grid electrodes, and a pair of symmetrically spaced anodes, the method of comparing phase differences oi' signals at least one of which is modulated in phase in accordance with intelligence to be transmitted, which includes the steps of applying one of the signals to the grid electrodes differentially whereby opposite potentials are simultaneously applied to the diilerent grids, applying the other signal to the grid electrodes in parallel whereby similar potentials are simultaneously applied to the different grids, and additively obtaining alternating current energy from the anodes of said tube.

14. Signal demodulating means comprising a thermionic tube of the cathode ray type having a cathode, control electrodes, anda plurality of anodes, means for impressing signal modulated energy on said control electrodes, a symmetrical output circuit connected between said anodes, and a regenerative coupling between said output circuit and said means for impressing energy on said control electrodes.

15. Means for demodulating electrical oscillations including, a cathode ray tube having a plurality of anodes, a plurality of control electrodes,`

CLARENCE W. HANSELL. 

